I'm reading Light on Life, The Yoga Journey to Wholeness, Inner Peace, and Ultimate Freedom by B.K.S. Iyengar.   Even if you don't practice "Iyengar" Yoga your practice is in some way influenced by his work.   An short exerpt that I've been inspired by the last few days:

 

"'Tapas'...the word implies intense, purifying heat, a fire that, like the alchemist's, transforms base metal into gold.  Imagination is the flickering flame, the coolest part of the fire.  Dancing flames give light to reveal shape, which in yoga terminology, is the subtle counterpart of fire.  What is an idea, a concept, but a shape in the mind?  The work before us is to blow on the fire with the bellows of tapas, so that it becomes intensely hot and transforms the shapes of mind into reality.  Asana practice brings mind and body into harmony for this task.  Your mind is always ahead of your body.  The mind moves into the future, the body the past, but the self is in the present.  The coordination between them that we learn in asana (posture practice) will enable us to turn our visions into the substance of our lives."